全文获取类型
收费全文 | 2073篇 |
免费 | 114篇 |
国内免费 | 4篇 |
专业分类
化学 | 1705篇 |
晶体学 | 20篇 |
力学 | 16篇 |
数学 | 205篇 |
物理学 | 245篇 |
出版年
2023年 | 26篇 |
2022年 | 100篇 |
2021年 | 117篇 |
2020年 | 75篇 |
2019年 | 70篇 |
2018年 | 64篇 |
2017年 | 38篇 |
2016年 | 117篇 |
2015年 | 74篇 |
2014年 | 97篇 |
2013年 | 135篇 |
2012年 | 131篇 |
2011年 | 155篇 |
2010年 | 99篇 |
2009年 | 88篇 |
2008年 | 143篇 |
2007年 | 97篇 |
2006年 | 101篇 |
2005年 | 88篇 |
2004年 | 75篇 |
2003年 | 50篇 |
2002年 | 40篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 20篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1961年 | 2篇 |
1960年 | 2篇 |
1887年 | 1篇 |
排序方式: 共有2191条查询结果,搜索用时 15 毫秒
961.
Florian Klappenberger Dr. Marta E. Cañas‐Ventura Dr. Sylvain Clair Dr. Stéphane Pons Dr. Uta Schlickum Dr. Zhi‐Rong Qu Dr. Thomas Strunskus Dr. Alessio Comisso Dr. Christof Wöll Prof. Harald Brune Prof. Klaus Kern Prof. Alessandro De Vita Dr. Mario Ruben Dr. Johannes V. Barth Prof. 《Chemphyschem》2008,9(17):2522-2530
We report on a multi‐technique investigation of the supramolecular organisation of N,N‐diphenyl oxalic amide under differently dimensioned environments, namely three‐dimensional (3D) in the bulk crystal, and in two dimensions on the Ag(111) surface as well as on the reconstructed Au(111) surface. With the help of X‐ray structure analysis and scanning tunneling microscopy (STM) we find that the molecules organize in hydrogen‐bonded chains with the bonding motif qualitatively changed by the surface confinement. In two dimensions, the chains exhibit enantiomorphic order even though they consist of a racemic mixture of chiral entities. By a combination of the STM data with near‐edge X‐ray absorption fine‐structure spectroscopy, we show that the conformation of the molecule adapts such that the local registry of the functional group with the substrate is optimized while avoiding steric hindrance of the phenyl groups. In the low coverage case, the length of the chains is limited by the Au(111) reconstruction lines restricting the molecules into fcc stacked areas. A kinetic Monte Carlo simulated annealing is used to explain the selective assembly in the fcc stacked regions. 相似文献
962.
Blesic M Lopes A Melo E Petrovski Z Plechkova NV Canongia Lopes JN Seddon KR Rebelo LP 《The journal of physical chemistry. B》2008,112(29):8645-8650
The aggregation behavior in aqueous solution of a number of ionic liquids was investigated at ambient conditions by using three techniques: fluorescence, interfacial tension, and (1)H NMR spectroscopy. For the first time, the fluorescence quenching effect has been used for the determination of critical micelle concentrations. This study focuses on the following ionic liquids: [Cnmpy]Cl (1-alkyl-3-methylpyridinium chlorides) with different linear alkyl chain lengths (n=4, 10, 12, 14, 16, or 18), [C12mpip]Br (1-dodecyl-1-methylpiperidinium bromide), [C12mpy]Br (1-dodecyl-3-methylpyridinium bromide), and [C12mpyrr]Br (1-dodecyl-1-methylpyrrolidinium bromide). Both the influence of the alkyl side-chain length and the type of ring in the cation (head) on the CMC were investigated. A comparison of the self-aggregation behavior of ionic liquids based on 1-alkyl-3-methylpyridinium and 1-alkyl-3-methylpyridinium cations is provided. It was observed that 1-alkyl-3-methylpyridinium ionic liquids could be used as quenchers for some fluorescence probes (fluorophores). As a consequence, a simple and convenient method to probe early evidence of aggregate formation was established. 相似文献
963.
Ventura B Barigelletti F Durola F Flamigni L Sauvage JP Wenger OS 《Dalton transactions (Cambridge, England : 2003)》2008,(4):491-498
The redox behaviour, optical-absorption spectra and emission properties of U-shaped and elongated disubstituted biisoquinoline ligands and of derived octahedral Fe(ii), Ru(ii), and Re(i) complexes are reported. The ligands are 8,8'-dichloro-3,3'-biisoquinoline (1), 8,8'-dianisyl-3,3'-biisoquinoline (2), and 8,8'-di(phenylanisyl)-3,3'-biisoquinoline (3), and the complexes are [Fe(3)(3)](2+), [Fe(2)(3)](2+), [Ru(1)(phen)(2)](2+), [Ru(2)(3)](2+), [Ru(3)(3)](2+), [Re(2)(py)(CO)(3)](+), and [Re()(py)(CO)(3)](+). For the ligands, the optical properties as observed in dichloromethane are in line with expectations based on the predominant (1)pipi* nature of the involved excited states, with contributions at lower energies from (1)npi* and (1)ILCT (intraligand charge transfer) transitions. For all of the Fe(ii), Ru(ii), and Re(i) complexes, studied in acetonitrile, the transitions associated with the lowest-energy absorption band are of (1)MLCT (metal-to-ligand charge transfer) nature. The emission properties, as observed at room temperature and at 77 K, can be described as follows: (i) the Fe(ii) complexes do not emit, either at room temperature or at 77 K; (ii) the room-temperature emission of the Ru(ii) complexes (phi(em) > 10(-3), tau in the micros range) is of mixed (3)MLCT/(3)LC character (and similarly at 77 K); and (iii) the room-temperature emission of the Re(i) complexes (phi(em) approximately 3 x 10(-3), tau < 1 ns) is of (3)MLCT character and becomes of (3)LC (ligand-centered) character (tau in the ms time scale) at 77 K. The interplay of the involved excited states in determining the luminescence output is examined. 相似文献
964.
Zarycz N Botek E Champagne B Sciannaméa V Jérôme C Detrembleur C 《The journal of physical chemistry. B》2008,112(34):10432-10442
Density functional theory (DFT) calculations have been performed to address the structure of nitroxide intermediates in controlled radical polymerization. In a preliminary step, the reliability of different theoretical methods has been substantiated by comparing calculated hyperfine coupling constants (HFCCs) to experimental data for a set of linear and cyclic alkylnitroxyl radicals. Considering this tested approach, the nature of different nitroxides has been predicted or confirmed for (a) the reaction of C-phenyl- N- tert-butylnitrone and AIBN, (b) N- tert-butyl-alpha-isopropylnitrone and benzoyl peroxide, (c) tert-butyl methacrylate polymerization in the presence of sodium nitrite as mediator, and (d) for the reaction of a nitroso compound with AIBN. Values of HFCC experimentally determined have been confirmed by DFT calculations. 相似文献
965.
966.
This paper describes an analytical method for trace element determination in bone tissues. The study of the influence of the
bone matrix showed that the addition of 25% ground bone to graphite powder with introduced impurities did not affect the analytical
signal of elements in the spectral excitation in a two-jet plasma. On basis of these investigations a method for direct multielement
analysis of bone tissues was suggested. The sample preparation procedure consisted in mixing powdered bone (particle size
30 μm or less) with a spectroscopic buffer (graphite powder plus NaCl) in ratio 1:3 or to a greater extent depending on the
analyte concentration. Reference samples based on graphite powder were used for construction of calibration curves. The NaCl
concentration in analyzed and calibration samples was 15 wt%. The effect of particle size was revealed from the determination
of Ba, Sr, and Mg. To eliminate this effect, treatment of the samples with nitric acid was proposed. The validation of the
technique was confirmed by comparison of the analysis results of a bone sample with those obtained by inductively coupled
plasma atomic emission spectrometry after wet acid digestion. The limits of detection estimated for 20 elements were the following
(μg g-1): 0.1 (Ag), 1.0 (Al), 1.0 (Ba), 0.1 (Be), 1.2 (Bi), 0.4 (Cd), 1.0 (Co), 0.2 (Cu), 0.6 (Cr), 1.9 (In), 2 (Fe), 0.3 (Ga), 0.4
(Mn), 0.4 (Mo), 0.7 (Ni), 1.0 (Pb), 0.7 (Sn), 0.8 (Tl), 5 (Sr), 1.0 (Zn). 相似文献
967.
A method employing the headspace single-drop microextraction (HS-SDME) is presented for the determination of essential oils in dried herbal leaves. By optimising the key experimental parameters, a linear response for the individual target compounds was obtained in the concentration range from LOQ to 4 mg/mL (r(2) = 0.9912-0.9998), with LODs from 3.3 up to 20.5 microg per 100 g of dried leaves, and the repeatability within the RSD of 2.1-8.9%. The HS-SDME-based procedure, enabling a rapid and simple analysis of essential oils in herbs, was applied to selected real samples (nine essential oils in four different samples) in combination with GC-FID identification and quantification of the target volatiles. 相似文献
968.
María E. Pérez Vitor A. S. Almodovar Javier E. Durantini Natalia S. Gsponer Andrés M. Durantini Augusto C. Tomé Edgardo N. Durantini 《Photochemistry and photobiology》2023,99(4):1131-1141
Diketopyrrolopyrrole (DPP) derivatives containing sulfonamide ( Sulfonamide-DPP ), pyridyl ( Dipyridyl-DPP ) and N-methylpyridyl ( MePyridyl-DPP ) substituents were assessed as antibacterial photosensitizers. Non-charged DPPs showed an intense absorption band centered at about 480 nm and green fluorescence emission (ΦF ~ 0.7) in acetonitrile. The absorption of MePyridyl-DPP was bathochromically shifted at 510 nm, with decreased fluorescence emission. Sulfonamide-DPP and Dipyridyl-DPP photosensitized the formation of O2(1Δg) (ΦΔ ~ 0.15–0.17), while the production induced by MePyridyl-DPP was at least 10 times lower. Furthermore, these DPPs produced a photoreduction of NBT similar to that of the control. Photodynamic inactivation induced by DPPs was first investigated at the single-bacterium level of Staphylococcus aureus attached to a surface. After 30 min irradiation, MePyridyl-DPP produced a complete eradication of the bacteria. In bacterial cell suspensions, dicationic DPP induced more than 7 log10 decrease in S. aureus cell survival after 30 min irradiation. Potentiation with iodide anions allowed a complete elimination of bacteria after 15 min therapy. This compound was also effective to eliminate S. aureus cells on biofilms. The results show that MePyridyl-DPP bearing two positive groups provides an amphiphilic character to the structure that improves the interaction with the cell envelop. This effect enhances the photocytotoxic activity of MePyridyl-DPP against bacteria. 相似文献
969.
Luo SC Mohamed Ali E Tansil NC Yu HH Gao S Kantchev EA Ying JY 《Langmuir : the ACS journal of surfaces and colloids》2008,24(15):8071-8077
Nanobiointerfaces were prepared based on an electrically conductive polyethylenedioxythiophene (PEDOT). Thin (<100 nm), ultrasmooth (roughness ( R(rms)) < 5 nm), and functionalized PEDOT films have been successfully electropolymerized using aqueous microemulsion. The microemulsion polymerization is found to be catalyzed in the presence of a low concentration of acid and allows for film formation from various functionalized ethylenedioxythiophenes (EDOTs) (e.g., EDOT-OH, C(2)-EDOT-COOH, C(4)-EDOT-COOH, C(2)-EDOT-NHS, EDOT-N(3)) and their mixtures. The nanobiointerfaces are compositionally tunable and controlled to deposit on selected electrode surfaces. They prefer orthogonal growth on patterned surfaces and are synthesized within seconds. These thin PEDOT films exhibit very low intrinsic cytotoxicity and display no inflammatory response upon implantation, making them ideal for biosensing and bioengineering applications. 相似文献
970.
Kalwarczyk T Ziebacz N Fiałkowski M Hołyst R 《Langmuir : the ACS journal of surfaces and colloids》2008,24(13):6433-6440
We study the separation in the binary and ternary mixtures of the water/surfactant C12E5/polymer PEG system. The phase separation in the mixtures at late stages is governed by two distinct mechanisms: the coalescence-induced coalescence and the droplet evaporation mechanism. We show that when the coalescence-induced coalescence process is globally terminated in the sample consisting of a dense system of domains, another mechanism, which we call the collective droplet evaporation, starts to dominate. It manifests itself as a front of "evaporating" domains, which propagates at constant speed in the system. We show that the collective evaporation is induced by the gravitational drift of large droplets. 相似文献